DE3689615T2 - Aromatic dicarboxylic acid polyamides. - Google Patents

Abstract

Polyamide resins are prepared from aromatic dicarboxylic acids and which are substantially free of dimeric or higher polymeric fat acids. The resins generally have improved alkaline water solubility or dispersibility having substantially lower solution viscosities than prior polyamide resins. The harder resins with their water solubility find particular utility as ink binders. The softer resins find utility as a film layer bonding two flexible substrates.

Description

Field of the invention

The invention relates to polyamide resins prepared from aromatic dicarboxylic acids and which are substantially free of dimeric or higher polymeric fatty acids. The resins, which have substantially lower solution viscosities than prior art polyamide resins, generally have improved solubility or dispersibility in alkaline water. The harder resins, with their water solubility, find particular use as printing ink binders. The softer resins find use as a film layer bonding two flexible substrates.

Background of the invention

Flexographic inks are solvent-based inks that are applied by rollers or blocks to flexible sheets or rollers of plastic films and paper. The practical aspects of using such ink resins and inks derived therefrom require that the polyamide resin must be soluble in alcoholic solvents and that such solubility must be achieved without impairing strength, adhesion and gloss.

Environmental concerns about the levels of volatile organic solvents in the atmosphere have led to the desire to use aqueous solutions containing less volatile organic solvents. To achieve the reduced levels of volatile organic solvents, the polyamide resins used as binders should have increased water solubility and still maintain the other desirable properties of polyamide resins such as those based on polymeric fatty acids.

U.S. Patent Nos. 3,253,940 and 3,224,893 discuss the polyamide resins of polymeric fatty acids used in the past in formulations employing alcoholic solvents, particularly ethanol, in which lacquers of the polyamides in alcoholic solvents were in the range of 35 wt.% nonvolatile solids.

The foregoing patents provided resins that could be used with the common alcoholic solvents. However, as environmental concerns were sought, efforts were made to suppress emissions such as those of the volatile alcoholic solvents. One means of reducing emissions was to provide water-reducible polymeric fatty acid polyamides as explained in U.S. Patent No. 3,776,865. As disclosed therein, this could be accomplished by acid-terminating the polymeric fatty acid polyamides using an acid component of the polymeric fatty acid and another co-dicarboxylic acid and an amine component comprising isophorone diamine alone or in admixture with common diamines such as alkylenediamines, e.g., ethylenediamine. Acid termination was achieved by using about 50-75 amine equivalents per 100 carboxyl equivalents. Varnishes of these resins in an alcoholic solvent such as n-propanol in the range of 40% non-volatile solids are disclosed.

Another U.S. patent, U.S. Patent No. Re. 28,533, dealing with polymeric fatty acid polyamides using lower aliphatic monobasic acids such as acetic and propionic acid with certain amine combinations, revealed somewhat lower solubility in ethanol up to 60%, although many were 50% or less.

FR-A-2 154 639 relates to polyamide resins wherein equivalent amounts of acid and amine are used to provide a substantially neutral polyamide of relatively high molecular weight to be used as a hot melt adhesive. Further polyamides to be used as a hot melt adhesive are disclosed in FR-A-1 559 478, wherein preferably equivalent amounts of acid (including polymeric fatty acids) and amine are used.

FR-A-2 407 228 also refers to a high molecular weight polyamide resin which is resistant to boiling water and which has low water absorption.

The resins according to these French patents are not soluble in aqueous solution.

As environmental protection requirements have become more stringent, further efforts have been made to provide resins that meet such standards. High solids coatings in the order of 55-60% and preferably above 60% formulated into pigmented inks will achieve the desired solvent emission standards to reduce solvent emissions.

U.S. Patent No. 4,508,868 discloses polyamides prepared from polymeric fatty acids and diamines comprising an unsaturated fatty acid monomer in the fatty acid component and using relative amounts of amine and carboxyl so as to provide an acid terminated product having an acid number in the range of 8-20 and preferably in the range of 10-15. Such products could be used in alcoholic ink varnishes at levels of 60% solids or more.

While the polyamide resins of polymeric fatty acids provide acceptable properties in most cases, they do not possess the desired water solubility or dispersibility when applied in inks or varnishes. Accordingly, attempts have been made to improve the hardness and water solubility of products containing even less volatile organic solvents. U.S. Application No. 701,903, filed February 15, 1985, by Whyzmuzis et al., was an attempt to overcome the disadvantages of the polymeric fatty acid polyamide resins. This patent application discloses polyamides that are substantially free of polymeric fatty acids and have improved water solubility when used in flexographic or gravure ink binders. While such resins generally provide acceptable products, opportunities still exist to improve the hardness or non-tacky properties of the resins.

Brief description of the invention

It has now been found that further improved polyamide resins which are substantially free of polymeric fatty acids and can be conveniently used as flexographic or gravure ink binders are provided by employing an aromatic dicarboxylic acid in the acid component. The use of the aromatic dicarboxylic acids provides resins with improved hardness or non-tackiness properties while retaining the advantageous properties of the prior resins such as those of US Patent No. 4,508,868 or US Patent Application No. 701,903 as mentioned above. Thus, the present invention provides water-soluble polyamide resin compositions having a solution viscosity of AA₁ according to the method of Gardner Holdt which are formed from a mixture of X equivalent % of an acid component and Z equivalent % of an amine component, wherein the acid component is an aromatic dicarboxylic acid alone or a mixture with an aliphatic dicarboxylic acid with 2-25 carbon atoms and the amine component comprises a diamine alone, a monoalkanolamine alone, or mixtures of diamine and monoalkanolamine and wherein the ratio of Z:X is less than 1 to provide a polyamide having an acid number greater than 35. The preferred polyamides are those wherein the ratio of Z:X is less than 0.9, more preferably in the range of 0.50 to 0.85, and most preferably in the range of 0.65 to 0.85.

When the diamine used is an alkylenediamine or a polyether diamine having an average molecular weight of over 250, a copolymerizing acid or amine is present in the acid or amine component and the polyether diamine comprises an excess of 25 equivalent % of the copolymerizing amine in the amine component.

In addition to providing the foregoing polyamide resins, the invention also provides binder compositions such as flexographic or gravure ink compositions containing such resins, aqueous solvents and color pigments. In addition to use in flexographic or gravure ink compositions, the polyamide resins of the invention also find application in surface coatings where harder, non-tacky coatings are desired, particularly where it is desired to apply such coatings from aqueous solutions of low solution viscosity, optionally with pigments. Furthermore, the softer resins can be used when it is desired to bond two flexible substrates where adhesion to both is desired.

Detailed description of the invention

The polyamide resins of the present invention are prepared by polymerizing a mixture of the amine component and the acid component. The resins are acid-terminated resins in that an excess of dicarboxylic acids in relation to on the amine component reactants. If it is desired to use a monobasic acid as a chain terminator, it should be used in limited or very small amounts (less than 10 and preferably less than 5 equivalent %) since its presence can adversely affect the properties of the polyamide resin. The ratio of the equivalents of amine component to the equivalents of acid component is less than 1, preferably less than 0.9, more preferably ranges from 0.50 to about 0.85 and most preferably from 0.65 to 0.85. Regarding the equivalents of the amine component, it is necessary to take into account the hydroxyl group of the alkanolamine which can also react with the carboxyl groups of the acid component and which can give a polyesteramide, i.e. a polyamide which also contains ester groups. Accordingly, when reference is made to the equivalents of the amine component, it is understood that both the hydroxyl and amine equivalents of the amine component are taken into account.

As mentioned above in the polyamide resins of the invention, an aromatic dicarboxylic acid is used either alone or in admixture with copolymerizing aliphatic dicarboxylic acids. Generally, the aromatic dicarboxylic acid used will contain 8-16 carbon atoms. Such acids include phthalic acid, isophthalic acid and terephthalic acid, as well as diphen- and naphthalenedicarboxylic acids, with isophthalic acid and terephthalic acid being the preferred acids.

The aliphatic dicarboxylic acids that can be used together with the aromatic dicarboxylic acid are those containing 2-25 carbon atoms in the longer chain acids, i.e. 13 and more, with the acids having 16-21 carbon atoms being most preferred. The dicarboxylic acids include not only the straight chain aliphatic acids, but also those having branched alkyl chains and alicyclic structures in the molecule as well.

Accordingly, the dicarboxylic acids include the common shorter chain acids beginning with ethanedionic and the common aliphatic dicarboxylic acids such as azelaic, adipic and sebacic acids. The class also includes longer chain dicarboxylic acids such as heptadecanedicarboxylic acid (a C19 acid) and acids obtained from the Diels-Alder reaction products of acrylic acid with a fatty acid having conjugated ethylenic unsaturation such as 2-n-hexyl-5-(7-carboxyl-n-heptyl)cyclohex-3-enecarboxylic acid (a C21 diacid), which can be purchased from Westvaco, Charleston Heights, SC as Westvaco diacid. Heptadecane dicarboxylic acids are well known and are prepared according to the known process of carboxylation of oleic acid. These acids are referred to in U.S. Patent No. 3,781,234, which in turn refers to German Patent No. 1,006,849 for the preparation of 1,8- or 1,9-heptadecane dicarboxylic acid.

As already indicated, the aromatic dicarboxylic acid is used alone or in a mixture with the aliphatic dicarboxylic acids. If the aliphatic dicarboxylic acid is used, it may be used in an amount of up to 50 equivalent % of the acid component or in an aromatic to aliphatic dicarboxylic acid equivalent ratio of 1:1. Stated another way, the acid component may accordingly comprise (a) 50-100 equivalent % of the aromatic dicarboxylic acid and (b) 0-50 equivalent % of the aliphatic dicarboxylic acid.

As noted above, the polyamides of the invention are prepared from blends substantially free of polymeric fatty acids. These polymeric fatty acids, which can be characterized as long chain polybasic acids, are described in U.S. Patent No. 3,776,865 and U.S. Patent No. 3,157,681. These polymeric fatty acids are derived from the polymerization of unsaturated fatty acids. If it is necessary to modify the resins of the present invention, Such polymeric fatty acids can be used in very small amounts, ie up to 5 equivalent %. Preferably no polymeric fatty acid should be used.

The diamines used to form the polyamide resins of the invention can be aromatic or aliphatic, cyclic and heterocyclic. Preferably, the diamine component contains at least one aliphatic diamine having 2-25 aliphatic carbon atoms or an alkanolamine, as will be discussed below. The preferred diamines can be divided into several preferred groups, mixtures of which can be used. Among the aromatic amines or the amines of the heterocyclic group, such as piperazine and xylylenediamine can be used. In the cycloaliphatic group, cyclic aliphatic diamines having 8-12 aliphatic carbon atoms, e.g., isophorone diamine, can be used.

Another preferred group includes short chain alkylenediamines which can be represented by the formula: H₂N-R-NH₂, in which R is an alkylene group having 2-8 carbon atoms. R can be branched or straight chain, with straight chain radicals being preferred. Specific examples of short chain alkylenediamines are ethylenediamine, diaminopropane, diaminobutane and hexamethylenediamine. Another group is the short chain polyether diamines which are commercially available and which are represented by the formula:

H₂N-R'-(O-R')x-O-R'-NH₂

wherein R' is an alkylene group having 2-6 carbon atoms, preferably an ethylene or isopropylene group, and X is an integer from 0-5, preferably 1 or 2, so as to give an average molecular weight of not more than 400 and preferably less than 250. Commercially available polyether diamines are Jeffamine D-230 and 400, which are described by the manufacturer as polyoxypropylene diamine.

The monoalkanolamines which can be used alone or in admixture with the aromatic, aliphatic or heterocyclic diamines in this invention are those containing 2-6 straight chain or branched chain carbon atoms which can be represented by the formula: OH-R"-NH2, where R" is an alkylene group having 2-6 carbon atoms. Specific examples of short chain monoalkanolamines are ethanolamine, propanolamine and butanolamine, with the ethanol and propanolamine products being preferred.

The resins are prepared from mixtures of a dicarboxylic acid component and an amine component by known methods for the polymerization of diacids and diamines to form polyamides. Generally, a mixture of the diacid component and the diamine component is heated to a temperature of 100-250°C in a vessel equipped to remove the by-product water formed in the amide-forming reaction, e.g., a vessel equipped with a distillation unit and a condenser to remove water from the reaction zone.

Typically, the reaction mixture is initially heated to lower temperatures to avoid any volatilization and loss of any reactant that may be employed, after which the temperature is raised to a higher reaction temperature. Thus, it is usual to heat to a temperature of 140ºC for 1 hour, then increase the temperature to 210-250ºC, and react for 1.0-3.0 hours, preferably under vacuum for the last hour.

The degree of polymerization of the mixture is controlled together with a selection of the amine: acid ratio to achieve a To provide polyamide with a high acid number. The acid number of the polyamide should be greater than 35 mg KOH/g sample, more preferably greater than 50 mg KOH/g sample, ie between 50 and 250 mg KOH/g sample, depending on the particular amine and acid formulation.

The polyamide resins of the invention form the binder compositions of the invention when dissolved in an aqueous solvent containing ammonia or an organic amine. The resin is added to the solvent in an amount of 30-40% resin solids based on the weight of the solvent. Examples of suitable organic amines include primary, secondary and tertiary amines which serve as a base for salt formation of the acid terminated polyamides. Particularly preferred organic amines are the dialkylaminoalkanols such as 2-(N,N-dimethylamino)ethanol and 2-(N,N-diethylamino)ethanol.

The organic amine is present in the aqueous solution in an amount sufficient to solubilize the selected polyamide resin. Generally, the organic amine will be present in the aqueous solution in an amount sufficient to theoretically neutralize the acid groups of the polyamide, i.e., the amount of organic amine is stoichiometrically equivalent to or greater than the acid value of the polyamide. For example, a 7.4 percent solution of dimethylaminoethanol is stoichiometrically equivalent to a polyamide resin having an acid number of 70 mg KOH/g sample used at a level of 40 percent resin solids. A large excess of organic amine should be avoided because retention of the organic amine in the cured binder can adversely affect the water resistance of the binder.

These binders are particularly suitable for flexographic or gravure ink compositions. These resins can also be suitable for other coating compositions where harder, non-tacky products are desired or in cases of softer, somewhat tacky products, for bonding two flexible substrates where adhesion to each substrate is desired. When used in printing ink compositions, the inks are prepared by dispersing a flexographic/gravure ink pigment into the binder composition of the invention.

The invention can be further illustrated by the following non-limiting examples in which all parts and percentages are by weight unless otherwise indicated. In the examples, polyamides according to the present invention are generally designated by Arabic numerals and the comparative examples are generally designated by a letter. Furthermore, in the examples, the terms, abbreviations and symbols have the following meanings:

IPA: 1,3-Isophthalic acid

PA: Propionic acid

EDA: Ethylenediamine

D-230: Jeffamine D-230 - polypropylenediamine, available from Texaco Chemical Company, with a molecular weight of 230

D-400: Jeffamine D 400 - polypropylene diamine with a molecular weight of 400

C₂₁: Westvaco C₂₁-diacid - 2-n-hexyl-5-(7-carboxyl-nheptyl)cyclohex-3-enecarboxylic acid

MEA: Monoethanolamine

HMDA: Hexamethylenediamine

T.Av.: Theoretical acid number

Act.Av.: Actual acid number

Am.V.: Amine number

OH V.: Hydroxyl number

SPºC: Softening point ºC (ball and ring)

P.S.: Physical condition

Sol.: Solubility

C3M-30: Solvent composition 75.2/15.9/5.8/3.1 - H₂O/n-propanol/dimethylethanolamine/NH₄OH

P.E.Wet.: 30% solid paint (resin plus solvent) wetted polyethylene

H₂O Tack: Resin alone develops stickiness when immersed in water

H₂O Resist: Films of dried lacquer on polyethylene subjected to 100 finger rubs with water after 30 minutes exposure

Disp.: Stable dispersion

Typical resin production

The resins described in the examples and summarized in Table I below were prepared by charging the acid and amine reactants shown in Table I to a reactor along with 1% of an 85% phosphoric acid solution as a catalyst. The reaction mixture was heated to 210°C to 250°C and was held at that temperature for 1 to 2.5 hours. The resulting resin had the properties shown in Table II; Comparative Example A, which had a Gardner Holdt solution viscosity of H-1, illustrates a composition as found in U.S. Application No. 701,903.

Examples 1-17 illustrate resins of the invention which are soluble in aqueous solutions and which find use as printing ink varnishes. Each of these solutions are very low solution viscosity products which have a solution viscosity in the range of water alone, ie, Gardner Holdt from AA₁. Examples 16 and 17, which are tacky, are resins which could be applied from aqueous solutions but are better suited to applications where tack is advantageous, e.g., in bonding two flexible substrates where adhesion to each substrate is desired. Table I Reactant equivalents Example

The physical properties of the resulting resin and the evaluation of the resin, particularly in paint solutions, with respect to a printing ink resin can be seen from Table II below. Table II Example yes no hard Disp. brittle Border sticky

Examples 1-17, summarized in Tables I and II, illustrate compositions that have low solution viscosity in aqueous solutions. Examples 1-13 are particularly desirable for ink varnishes for flexographic/gravure inks that provide hard resins. Examples 14 and 15, which still have low tack, are suitable for printing ink applications and have improved low solution viscosity compared to Example A.

Other resin series have been produced and they represent isophthalic acid-based polyamides that offer a range of properties from very hard (although not soluble in aqueous alkaline solutions) to semi-solid, semi-liquid or liquid products which find application in other fields requiring water solubility other than inks or ink varnishes. Such other resins can provide coatings either of the 100% solid type or formed from the solvent system where such is acceptable. Their compositions and properties can be seen from Tables III and IV below. Table III Reactant equivalents Example * IPA is added in two steps Table IV Examples sintered very hard hard slightly liquid none yes no

Example 23

Example 8 was repeated except that the reaction time at 210°C was 3.5 hours, with vacuum (10 mm) being applied in the last hour. Working under vacuum resulted in a reduction in the hydroxyl number, with the other properties remaining essentially unchanged.

This can be seen from Table V below, in which the values of Example 8 are included for comparison. Table V Example yes

Claims (20)

1. Water-soluble polyamide resin having a solution viscosity of A-A₁ according to the Gardner Holdt method, prepared by polymerizing a mixture of X equivalent % of an acid component with an amount of polymeric fatty acid of up to 5 equivalent % selected from: an aromatic dicarboxylic acid alone or in admixture with up to 50 equivalent % of a copolymerizing aliphatic dicarboxylic acid containing 2-25 carbon atoms and Z equivalent % of an amine component, wherein the ratio of Z to X is less than 1 to provide an acid number greater than 35 mg KOH/g sample, wherein the amine component is selected from the group consisting of: a) a diamine b) a monoalkanolamine and c) copolymerizing mixtures thereof and further with the proviso that when the diamine is an alkylenediamine or a polyetherdiamine having an average molecular weight of greater than 250, a copolymerizing acid or a copolymerizing amine is also present in the acid or the amine compound and with the proviso that the polyetherdiamine comprises 25 equivalent % excess of the copolymerizing amine in the amine component. 2. Polyamide according to claim 1, wherein the ratio of Z to X is 0.50 to 0.85. 3. Polyamide according to claim 1, wherein the acid component contains 50-100 equivalent % of the n aromatic dicarboxylic acid and 0-50 equivalent % of an aliphatic dicarboxylic acid having 2-25 carbon atoms. 4. Polyamide according to claim 3, wherein the aliphatic dicarboxylic acid has 16-21 carbon atoms. 5. Polyamide according to claim 4, wherein the aliphatic dicarboxylic acid is heptadecane dicarboxylic acid. 6. Polyamide according to claim 4, wherein the aliphatic dicarboxylic acid is 2-n-hexyl-5-(7-carboxyl-n-heptyl)cyclohex-3-enecarboxylic acid. 7. Polyamide according to claim 3, wherein the aromatic dicarboxylic acid is isophthalic acid. 8. Polyamide according to claim 1, wherein the diamine is an aliphatic diamine having 2-25 carbon atoms. 9. Polyamide according to claim 8, wherein the diamine is an alkylene diamine in which the alkylene group contains 2-8 carbon atoms. 10. Polyamide according to claim 8, wherein the diamine is ethylenediamine. 11. Polyamide according to claim 8, wherein the diamine is hexamethylenediamine. 12. Polyamide according to claim 8, wherein the diamine is a polyether-diamine having an average molecular weight of not more than about 400. 13. Polyamide according to claim 12, wherein the polyetherdiamine has a molecular weight of less than 250. 14. Polyamide according to claim 1, wherein the monoalkanolamine has 2-6 carbon atoms. 15. Polyamide according to claim 14, wherein the alkanolamine is ethanolamine. 16. A binder composition comprising a polyamide resin according to claim 1 and an aqueous solvent containing ammonia and an organic amine. 17. Polyamide according to claim 1, wherein the aromatic acid is isophthalic acid, the aliphatic dicarboxylic acid is 2-n-hexyl-5-(7-carboxyl-n-heptyl)cyclohex-3-enecarboxylic acid, the aliphatic diamine is ethylenediamine and the alkanolamine is ethanolamine. 18. Polyamide according to claim 1, wherein the aromatic acid is isophthalic acid, the aliphatic dicarboxylic acid is 2-n-hexyl-5-(7-carboxyl-n-heptyl)cyclohex-3-enecarboxylic acid, the aliphatic diamine is hexamethylenediamine and the alkanolamine is ethanolamine. 19. The polyamide of claim 1, wherein the aromatic acid is isophthalic acid, the aliphatic dicarboxylic acid is 2-n-hexyl-5-(7-carboxyl-n-heptyl)cyclohex-3-enecarboxylic acid, the aliphatic diamine is polyetherdiamine having an average molecular weight of not more than about 400, and the alkanolamine is ethanolamine. 20. A printing ink varnish composition comprising a polyamide resin according to claims 1 to 19 and an aqueous solvent containing ammonia and an organic amine.